ATmega16U4 datasheet(277/408 Pages) ATMEL

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277

7766D–AVR–01/09

ATmega16U4/ATmega32U4

22.15.2

CRC Error

A CRC error can occur during OUT stage if the USB controller detects a bad received packet. In

this situation, the STALLEDI interrupt is triggered. This does not prevent the RXOUTI interrupt

from being triggered.

22.16 Overflow

In Control, Isochronous, Bulk or Interrupt Endpoint, an overflow can occur during OUT stage, if

the host attempts to write in a bank that is too small for the packet. In this situation, the OVERFI

interrupt is triggered (if enabled). The packet is acknowledged and the RXOUTI interrupt is also

triggered (if enabled). The bank is filled with the first bytes of the packet.

It is not possible to have overflow error during IN stage, in the CPU side, since the CPU should

write only if the bank is ready to access data (TXINI=1 or RWAL=1).

22.17 Interrupts

The next figure shows all the interrupts sources:

Figure 22-4. USB Device Controller Interrupt System

There are 2 kind of interrupts: processing (i.e. their generation are part of the normal processing)

and exception (errors).

Processing interrupts are generated when:

• VBUS plug-in detection (insert, remove)(VBUSTI)

• Upstream resume(UPRSMI)

• End of resume(EORSMI)

• Wake up(WAKEUPI)

• End of reset (Speed Initialization)(EORSTI)

• Start of frame(SOFI, if FNCERR=0)

• Suspend detected after 3 ms of inactivity(SUSPI)

Exception Interrupts are generated when:

• CRC error in frame number of SOF(SOFI, FNCERR=1)

UPRSMI

UDINT.6

UPRSME

UDIEN.6

EORSMI

UDINT.5

EORSME

UDIEN.5

WAKEUPI

UDINT.4

WAKEUPE

UDIEN.4

EORSTI

UDINT.3

EORSTE

UDIEN.3

SOFI

UDINT.2

SOFE

UDIEN.2

SUSPI

UDINT.0

SUSPE

UDIEN.0

USB Device

Interrupt

ATmega16U4 Datasheet(PDF) 277 Page - ATMEL Corporation

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